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Help! My CPU is starved. What do I feed it?

Scarlet O'Hara once said "I'm going to live through this and when it's all over, I'll never be hungry again." That was a story and era before computers. These days our computers can become starved, at least the Java (tm) virtual machine (JVM) can. Performance is a key concern for everyone. When users have to wait, they are discouraged and either become distracted or they go somewhere else. Keeping a system running smoothly is key. Every now and then systems will have a slow spot. However, when it continuously impacts users, this issue must be investigated. For this article, I am focusing on the following example outputs seen in an JVM SystemOut.log. These examples came from an IBM Business Process Manager SystemOut.log file.

DCSV0004W: DCS Stack DefaultCoreGroup at Member PCCell01\PCNode01\BPM751PDEV.AppTarget.PCMNode01.0: Did not receive adequate CPU time slice. Last known CPU usage time at 12:23:55:452 CST. Inactivity duration was 31 seconds.

What does CPU Starvation mean?
CPU Starvation means that the JVM had to wait for processing time! Some other process took 100% of the CPU and the JVM did not work. Twenty-three seconds is a long time for a server to wait. In some examples, I have seen the wait time as high as 70 seconds.

Where is all the CPU time going?There are two places to look. One is on the system itself. Is there a process on the operating system that has run away and is running at 99%? A simple top command combined withkill -3 command on Linux operating systems or the Task Manger (2) on Windows operating systems can help. If there is another application on the server that became hung and is taking all the CPU time, investigate and stop the process.

If the operating system does not have any extra processes and you see CPU starvation, most likely the server is a guest operating system on a virtual environment. What this means is the larger virtual infrastructure does not have enough CPU time to give all of the virtual machines it controls. Contact your virtual machine provider or internal sysops team to start investigating the overall health of the virtual system. Other virtual machines in the environment might be using the system heavily and need to move to a different server. Another option would be to dedicate CPU usage rather than sharing, which is default. We have a document that offers links to other documents to consider when you are running J2EE applications and databases in a virtual environment.